Filtering apparatus

ABSTRACT

A vertical vessel has a filter bed disposed in its lower portion for normal filtering of solid particulates from contaminated liquid passed down through the bed. Vertical passages are formed to extend below the upper surface of the filter bed with a layer of smooth-surfaced bodies arranged to reduce the cross-sectional area of the vessel to impart desired velocity to the particulates in the liquid.

United States Patent Isaac Paul Mail Tulsa, Okla.

Aug. 8, 1969 Continuation-impart of Ser. No. 737,721, July 17, 1968, nowabandoned Jan. 5, 1971 Combustion Engineering, Inc.

New York, N.Y.

a corporation of Delaware lnventor Appl. No. Filed Patented AssigneeFILTERING APPARATUS 4 Claims, 2 Drawing Figs.

11.8. CI.... 210/275 Int. Cl 801d 23/10 Field of Search 210/ 80,

[56] References Cited UNITED STATES PATENTS 2,115,232 4/1938 Pflanz210/279 2,559,936 7/1951 Buffle 210/274 2,855,364 10/1958 Roberts...210/274X 3,202,286 8/1965 Smit 210/290X 3,260,366 7/1966 Duffet al.2l0/274X 3,276,585 10/1966 Kalinske 210/279X Primary Examiner-Samih N.Zaharna Attorney-Arthur L. Wade ABSTRACT: A vertical vessel has a filterbed disposed in its lower portion for normal filtering of solidparticulates from contaminated liquid passed down through the bed.Vertical passages are formed to extend below the upper surface of thefilter bed with a layer of smooth-surfaced bodies arranged to reduce thecross-sectional area of the vessel to impart desired velocity to theparticulates in the liquid.

OUTLET/ F/LTERED WATER 4 /NLET/ WATER TO BE FILTERED SAC/(WASH OUTLETPATENTEU JAN 512m 3552.573

/IVLET/ WATER TO BE F/LTERED INLET/GAS BACKWASH OUTLET v 0 QUTL ET/1F AF/LTERED A 4-l/VLET/ GAS INVENTOR.

\ ISAAC PAUL MAIL m m-BACKWASH m INLET /4 l5 A ATTORNEY FILTERINGAPPARATUS This application is a continuation-in-part of US. Pat.application Ser. No. 737,721 filed Jun. 17, 1968, and now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention The presentinvention relates generally to filtering apparatus and more particularlyis directed to improvements in filtering apparatus of the downfiow type;that is, apparatus in which the liquid to be filtered is passeddownwardly through a filter bed of granular solids.

2. Description of the Prior Art In filtering apparatus presently in use,the liquid to be filtered and backwash liquids have been passed bothupwardly as well as downwardly through a filter bed of granular solids.

. There are advantages and disadvantages associated with each flowpattern.

. It is presently accepted that with a downflow pattern, theparticulates are removed from the liquid near the upper surface of thebed and collect in a cake" which is supported by the lower bed. Thiscake quickly increases the pressure drop in the downflowing liquid whichis a common index for limiting the filter cycle.

It is also presently accepted to backwash a filter bed within a vesselby continuously passing washing liquid through the bed in a directionopposite to the direction of filtering flow. The velocity of the liquidmust be great enough to expand the bed so as to dislodge .the filteredparticulates from the bed material. The total quantity of liquidrequired to return the bed to serviceable cleanliness is large.

SUMMARY OF THE INVENTION A principal object of the invention is todirect liquid to be filtered downwardly into a bed of granular materialand impart enough kinetic energy to the particulates for them toovercome the frictional forces imposed upon them by the surface of thegranular material. The particulates are thus caused to penetrate intothe bed a desired distance.

Another object is to jet particulates downward into a bed of granularmaterial so the particulates will penetrate the bed a desired depth andthen backwash the bed with fluids directed upward through the bed. I

Another object is to backwash the bed of granular material in a batchoperation and employ gas bubbles to agitate the bed material to aid indislodgment of particulates deposited in the bed.

The present invention contemplates a vessel having a bed of solidgranular material supported therein and arranged to receive a downwardflow of liquid from which it is desired to remove particulates. Astructure is mounted near the upper portion of the bed which will formmultiple vertical passages extended below the upper surface of the bedand whose total cross sectional area is substantially less than thecross-sectional area of the vessel. This reduction of thecross-sectional area results in the downflowing liquid increasing invelocity as it flows through the multiple passages. The increasedvelocity imparts to the particulates sufficient kinetic energy to causethem to penetrate into the bed a predetermined depth.

The invention further contemplates a unique method of cleaning the bedof particulates removed from filtered liquid. The bed is physicallyarranged spaced from the upper end of its vessel. Backwash liquid isthen passed upwardly through the bed to partially fill the space above.the bed. Gas bubbles are concurrently passed up through the'bed with theliquid to facilitate agitation of the bed which will dislodgeparticulates. After the space is partially filled with backwash liquidthe supply of gas is discontinued. The flow of backwash liquid iscontinued to purge the bubbles from the bed. Any dislodged bed materialis settled back into the bed. The liquid above the bed, with theparticulates entrained therein, is then removed. The cycle may berepeated until the particulate contamination of the bed has beensatisfactorily reduced.

Other objects, advantages and features of this invention will becomeapparent to one skilled in the art upon consideration of the writtenspecification, appended claims, and attached drawing, wherein;

FIG. 1 is a sectiohed sdhematic elevation of a filtering apparatusincluding the present invention; and

FIG. 2 is a plan view of FIG. 1 taken along the line 2-2.

DESCRIPTION OF THE PREFERRED EMBODIMENT BASIC STRUCTURAL ARRANGEMENTFIG. 1 discloses the subject invention embodied in the filteringapparatus generally identified bythe numeral 1. All of the structure ofthe apparatus centers about the vertically extended vessel 2. Thefiltering apparatus disclosed herein is of the downflow type. The rawinfluent is introduced into vessel 2 through conduit 3 for downwardpassage through filter bed 4, while the effluent filtrate is withdrawnfrom the base of vessel 2 through conduit 5. Also within-the vessel 2 isa layer of smooth-surfaced bodies 6 supported by a'wire mesh screen 7and a perforated support structure 8 for bed 4.

The contaminated, or raw, influent entering vessel 2 through conduit 3is given a predetermined flow rate. Since the velocity of the influentthrough the filtering medium is the critical variable in the design ofthe apparatus, the total crosssectional area of the flow paths to thetop surface of the filter bed 4 between bodies 6 (and hence the diameterof the vessel) is sized dependent upon this flow rate.

TESTS OF A CONVENTIONAL SYSTEM Tests were conducted using a filtermedium of granular solids now commonly employed in treating waterassociated with oil production and water produced from water supplywells for injection purposes in secondary recovery operations. Theparticulate material and size was that also found in such producedwaters.

It was observed during this testing that flow velocity normallydeveloped allowed the particulates to form a filter cake of lowpermeability to the influent on the top surface of the filter medium.The filter medium then became merely a support for this filter cake, andthe cake, in effect, became the filter medium. These velocities areconventionally less than 2 ft./min., and were ordinarily 0.3 to 0.5ft./min. v p

This continuing buildup of a filter cake on top of the medium results inan increasing pressure differential across the filtering apparatus, adecreasing throughput, and the need for frequent cleaning of the filter.I

BASIC FILTERING OPERATION The influent moves downwardly through thevessel 2 to the layer of smooth-surfaced bodies 6 supported by wire meshscreen 7. Screen 7 extends across the cross-sectional area of vessel 2and is situated below the top surface of the filter bed The layer ofbodies 6 forms a restriction to the flow of fluid through the fulldiameter of vessel 2. The influent must fiow through the paths formed bythe spaces between the bodies. These spaces form restrictive paths tothe flow and, in effect, act as jets or nozzles. This jetting actionincreases the flow velocity of the influent at the surface of the filtermedium 4 into a desired range.

Experiment established that the lower of the bodies 6 must be at leastpartially below the upper surface of the filter bed as shown in FIG. 1.From another view, the upper surface must extend up into the restrictivepaths formed by the spaces between the bodies 6 which act as jets ornozzles. If the bed surface is at, or below, the lower surface formed bybodies 6 the objectionable filter cake will buildup on the top of thefilter bed with the disadvantages found in the prior art. I

With the bed 4 and bodies 6 in correct positional relation, the desiredrange of flow rate of the influent imparts increased kinetic energy tothe particulates ,in the liquid and drives the particulates below theupper boundary of the filter medium.

At the surface of the filter bed, the bed does become saturated zonescreated by the particular flow velocity anticipated.

The bodies 6 function to reduce the cross-sectional area of the conduit(vessel 2) at the upstream surface boundary of the filter 'medium. Thisreduction in area increases the flow velocity of the contaminatedinfluent at this boundary, and causes the influent to move across theboundary region and into the medium.

Also, although spherical bodies 6 are disclosed, it is ap- I parentthnt'uther means are available to impart the desired "velocity gain tothe influent at the upper boundary of the filter bed. Although there aremany forms this structure could take tocarry out the objectives of theinvention, they should all produce a jetting effect which will drive theparticulates down into the bed and permit the ready return of displacedbed particles. Further, the upper boundary of the bed must extend upinto the passages formed by the structure producing the jetting effectto obviate formation of a filter cake.

It is obvious that the smooth-surface bodies 6 could take a variety ,ofshapes and materials. For example, they could be oblate or elongatespheroidal, or irregularly rounded (as smooth river stones). They couldbe formed from ceramic, glass, plastic, or metallic material. It is onlyimperative that they reduce the cross-sectional area of vessel 2sufficiently to impart adequate velocity to the flow, without themselvesbeing so small or so rough-surfaced as to initiate the filtering action.

:lt is noted that flow velocities above a certain value will expand ordisrupt the granular or sand-type filter medium depicted in FIG. 1.Velocities in this range exert sufficient pressure on the filter bedsurface to produce a coning, channeling, or drilling effect which willreduce the effectiveness of the filter bed. Velocities on the order of 7ft./min. (the high range of those tested) did not expand or disrupt thefilter medium under test, however.

BACKWASHING After the bed 4 is saturated with particulates by the novelarrangement disclosed above, the filtered material entrained in the bedmust be periodically removed. it has been common practice to simplyintroduce a liquid beneath the bed and flow the liquid upward with avelocity sufficient to dislodge the particulates. Gas has also beenintroduced up through the bed to agitate it and thereby loosen the bondbetween the particulates and the bed material. Some expansion of the bedtakes place and the velocity must be carefully controlled to avoidlosing a significant portion of the bed material entrained in thebackwash liquid. The present invention includes a method which providesthe upflowing backwash liquid, with agitating gas, but withoutsignificant loss of bed material. Further, the quantity of backwashliquid required is low and the rate of flow of this liquid can be keptquiet low.

Fundamentally, the method of the present'invention includes employing anumber of backwash cycles. A predetermined amount of liquid is passed upthrough the bed 4 to a predetermined level above the bed. Gas is usedconcurrently with the backwash liquid and/or in sequence with it. Thepredetermined amount of backwash liquid above the bed, with particulatematerial swept from the bed below, is then removed. Another amount ofbackwash liquid is again employed in the same manner and removed. Thiscycle is repeated enough times to reduce the bed contamination to thelevel desired for filtering service.

More specifically, referring to FIG. 1 when bed 4 is saturated byparticulates the flow, .of liquid to be filtered is terminated. A valve9 is indicated in conduit 3 for thiscontrol of flow into vessel 2.

The next step is to evacuate the upper-portion of vessel 2 of liquiddown to the bed 4. Horizontal index line A indicates this level near thetop of the bed 4-b'od'e6'. Outlet conduit 10 is shown as available forthis purpos' valve ii in the 'conduit providing the control. 3

Valve Ill is opened and the liquid shave the sea {will flow out conduit10 if the conduit is filled with liqdi'dl However, if necessary to primethis siphon system, gasf' 'canbe applied to the upper portion of vessel2 through co'ndu'it" 12. Valve 13 is provided in conduit 12 for controlThe pressure of the gas will force the liquid up conduit 10 and throughvalve 11. i

A backwash liquid, from a same. not shown, is next conducted into thelower portiohof vessel 2. Conduit 5 could be used for this purpose, butseparate conduit 14 is shown to give clarity to the disclosure. Valve 15is indicated in conduit 14 for this control.

Valve 11 in conduit 10 is closed, so the backwash liquid travels upthrough the bed 4 to dislodge particulate material from the bed. Gas isalso flowed up bed 4. This gas is conducted into vessel 2 throughconduit 16. This conduit is disclosed as arranged to introduce the gasinto the backwash liquid of conduit 14 to back upthe concept of flowingthe gas concurrently with the backwash liquid. Valve 17 is provided inconduit 16 for control. The precise arrangement of these conduits andvessel 2 is not disclosed to limit the invention. The concept is toflow'an'amount of backwash liquid and gas up through bed 4 to raise theliquid level from level A to'ievel' B. Gas is to be used to supplementthe agitating effect of the liquid. The gasmay be used concurrent withthe liquid or in sequence with it. After the agitation has driven amaximum amount of particulates into the liquid between levels A and 3,.additional backwash liquid is introduced through conduit 14 to flush thegas from the bed.

The higher liquid level is indicated at C, substantially the remainingportion of the vessel 2. The goal is to provide enough backwash liquidto flush the gas from bed 4 so that any bed material carried up intothis vessel space can settle back to bed 4 by gravity. If the gas werenot positively flushed from the bed, it would continue to break out andtend to retard-settlingof the bed material.

With level C reached by the backwash liquid in vessel 2, all fluids intothe vessel are shut off for a period of time. Gravity causes the bedmaterial to settle; this relatively fine material will slide over thesmooth surface of bodies 6 and into the bed 4. There remains theparticulate material dislodged into the backwash liquid and entrained inthis liquid between levels A and C. The next step is to simply removethis material and go through another cycle of backwashing.

Valve 11 is opened and the contaminated backwash water is drawn from thevessel 2 at level A through the lower end of conduit section18 which isthe internal end of conduit 10 inserted into vessel 2. Conduit 10 isformed with section 18 extending downwardly to return any bed materialto the vessel and prevent buildup in conduit 10 which might obstruct theoutlet. This run of conduit upward will give a measurable opportunityfor gravityto become effective during the settling period followingagitation.

This method of running a batch of backwash liquid up through-bed 4 canbe repeated as often as required to clean bed 4. Obviously the valvescontrolling the conduits can be au tomated to carry out this method ofcleaning. The positive, batch removal of backwash liquid requires lesstotal liquid than would the continuous flow of such liquid to firstpurge the bed and then sweep the vessel above the bed clean.

From the foregoing it will be seen that this invention is one .welladapted to attain all of the ends and objects herein set forth, togetherwith other advantages which are obvious and which are inherent to theapparatus.

it will also be seen that certain features and subcombinations are ofutility and may be employed without reference to other features andsubcombinations. This is contemplated by and is within the scope of theinvention.

As many possible embodiments may be made of the invention withoutdeparting from the scope thereof, it is to be understood that all matterherein set forth or shown in the accompanying drawing is to beinterpreted as illustrative and not in a limiting sense.

lclaim:

l. A filtering apparatus of the downflow type, including:

a vessel containing a filter bed of granular solids which are staticduring normal filtering operation;

inlet and outlet means connected to the vessel to respectively supply aliquid having particulate solids suspended therein to the vessel andremove filtered liquid from the vessel at vertically spaced apartlocations so that the liquid to be filtered is passed downwardly throughthe filter bed;

a plurality of independently movable bodies extended horizontally acrossthe cross-sectional area of the vessel and down into the top of the bedduring normal filtering operation, the bodies arranged to providevertical passageways for the liquid to be filtered to pass down into thefilter bed at a predetermined minimum velocity;

means positioned below the top surface of the filter bed to support andretain the bodies in their prescribed relation to the bed during eachphase of the filtering operation; and

whereby the downward velocity of the particulates suspended in theliquid carries the particulates down into the filter bed and the buildupof the particulates into a cake on the upper surface of the filter bedis obviated.

2. The filtering apparatus of claim 1, including:

a supply of backwash liquid; and

means to connect the backwash liquid to the vessel in an arrangement toflow the liquid up through the filter bed in removal of the particulatesdeposited on the bed.

3. A filtering apparatus of the downflow type, including:

a vessel containing a filter bed of granular solids which are staticduring normal filtering operation;

inlet and outlet means connected to the vessel to respectively supply aliquid having particulate solids suspended therein to the vessel andremove filtered liquid from the vessel at vertically spaced apartlocations so that the liquid to be filtered is passed downwardly throughthe filter bed;

a foraminous support structure extended horizontally across thecross-sectional area of the vessel below the top of the bed duringnormal filtering operation;

a layer of smooth-surfaced bodies arranged on the upper side of thesupport to provide vertical passageways extended below the top of thebed for the liquid to be filtered to pass down into the filter bed at apredetermined minimum velocity; and

whereby the downward velocity of the particulates suspended in theliquid carries the particulates down into the filter bed and the buildupof the particulates into a cake on the upper surface of the filter bedis obviated.

'4. The filtering apparatus of claim 3, including;

a supply of backwash liquid; and

means to connect the backwash liquid to the vessel in an arrangement toflow the liquid up through the filter bed in removal of the particulatesdeposited on the bed.

1. A filtering apparatus of the downflow type, including: a vesselcontaining a filter bed of granular solids which are static duringnormal filtering operation; inlet and outlet means connected to thevessel to respectively supply a liquid having particulate solidssuspended therein to the vessel and remove filtered liquid from thevessel at vertically spaced apart locations so that the liquid to befiltered is passed downwardly through the filter bed; a plurality ofindependently movable bodies extended horizontally across thecross-sectional area of the vessel and down into the top of the bedduring normal filtering operation, the bodies arranged to providevertical passageways for the liquid to be filtered to pass down into thefilter bed at a predetermined minimum velocity; means positioned belowthe top surface of the filter bed to support and retain the bodies intheir prescribed relation to the bed during each phase of the filteringoperation; and whereby the downward velocity of the particulatessuspended in the liquid carries the particulates down into the filterbed and the buildup of the particulates into a cake on the upper surfaceof the filter bed is obviated.
 2. The filtering apparatus of claim 1,including: a supply of backwash liquid; and means to connect thebackwash liquid to the vessel in an arrangement to flow the liquid upthrough the filter bed in removal of the particulates deposited on thebed.
 3. A filtering apparatus of the downflow type, including: a vesselcontaining a filter bed of granular solids which are static duringnormal filtering operation; inlet and outlet means connected to thevessel to respectively supply a liquid having particulate solidssuspended therein to the vessel and remove filtered liquid from thevessel at vertically spaced apart locations so that the liquid to befiltered is passed downwardly through the filter bed; a foraminoussupport structure extended horizontally across the cross-sectional areaof the vessel below the top of the bed during normal filteringoperation; a layer of smooth-surfaced bodies arranged on the upper sideof the support to provide vertical passageways extended below the top ofthe bed for the liquid to be filtered to pass down into the filter bedat a predetermined mInimum velocity; and whereby the downward velocityof the particulates suspended in the liquid carries the particulatesdown into the filter bed and the buildup of the particulates into a cakeon the upper surface of the filter bed is obviated.
 4. The filteringapparatus of claim 3, including; a supply of backwash liquid; and meansto connect the backwash liquid to the vessel in an arrangement to flowthe liquid up through the filter bed in removal of the particulatesdeposited on the bed.